Keeping CSS kosher requires a lot more code, and also assumes browser compatibility. According to CanIUse, about 7 percent of browser usage globally does not support CSS transitions, and half of that comes from Opera Mini, which Jacques (hi, Jacques!) says it's OK to ignore. So that leaves us with 3 percent global usage, or 5.6 percent U.S. (IE 8 and 9 users) unsupported.

So why keep CSS kosher if: 1) It requires more code, and; 2) It leaves out a small but actual percentage of users on unsupported browsers?

First, it makes it easier to maintain your code if you keep all styling separate. This I know to be true from experience... painful experience.

Second, Jacques says it is way more performant to keep CSS kosher because then your computer will offload transitions to the GPU, which is built to handle tasks like that.

So, when it comes down to it, your decision tree would be:

Do I have to support IE 8 and/or IE 9 users?

Yes: Use jQuery methods in your app.js file. Maybe eat a ham sandwich, and wash it down with milk while you're at it.